In the event of a loss-of-coolant accident, a nuclear reactor core may overheat, its fuel rod casings and nuclear fuel within these casings being capable of reaching temperatures causing melting and the formation of a falling core melt retaining its residual heat and decay heat. Such a falling core melt must be contained before it can contact and possibly melt through the bottom of the pressure vessel containing the core.
German Offenlegungsschrift No. 2,035,089 suggests a reactor core melt containment receptacle having water-cooled bottom and side walls. A water tank positioned above the receptacle connects with the inlets of water cooling pipes in its walls, the outlets for the pipes connecting with a standpipe which extends upwardly to above the level of this water tank. A core melt falling into this receptacle heats the water which by thermo-siphon action rises in the standpipe with the cold water descending from the tank.
The above receptacle is not suitable for use under the core of a high power breeder reactor. In this case the mass of the core and the residual and decay heat are so large that the bottom and side wall cooling alone cannot effectively abstract the heat with necessary rapidity. The receptacle must be deep to contain the core melt volume and removal of the interior heat from the melt by the water-cooled bottom and side wall is not adequate. This results in the discharged water being in the form of steam which rises and escapes from the standpipe to fill the reactor containment structure, which is very undesirable. Upward radiation of heat from the top of the core melt is intense and may possibly damage the heavy structural elements required for support of the core.